Device and method for the evaporative deposition of a coating material

ABSTRACT

According to a first aspect, the present invention relates to a device for depositing a high temperature superconductor onto a substrate in vacuum comprising a refilling device for containing a stock of high temperature superconductor material, an evaporation device, that evaporates the high temperature superconductor material within an evaporation zone by means of an energy transferring medium, and a conveyor that transports the high temperature superconductor material continuously from the refilling device to the evaporation zone in such a way that the high temperature superconductor material delivered into the evaporation zone is evaporated essentially without residues. According to a further aspect, the present invention relates to a method to evaporate a high temperature superconductor coating onto a substrate in vacuum, comprising the steps of continuous delivery of granular high temperature superconductor material into an evaporation zone and the operation of a beam of an energy transferring medium, so that the delivered granulate is evaporated in the evaporation zone essentially without residues.

1. TECHNICAL FIELD

The present invention relates to a device and a method for evaporating acoating material in vacuum ambient, particularly for the fabrication ofcoatings comprising complex inorganic compounds like high temperaturesuperconductors.

2. STATE OF THE ART

Thin films of complex inorganic compounds, e.g. oxides, nitrides,carbides or alloys of various cations, serve as functional coatings orsurface hardening in many applications in electronics, optics andmechanical engineering. For example films of PZT(Lead-zirconium-titanate) ceramics or BaTiO₃ are used for ferroelectricsensor elements or data memories with high dielectric constant. Thinepitaxial layers of RBa₂Cu₃O₇ (R=yttrium or a rare earth element) becomesuperconducting at low temperatures and can be used e.g. incommunication technology for highly selective radio frequency filters,or deposited on flexible metal tapes for conducting electrical currentwithout losses.

For the economic use for many of these applications large areas or longlengths (coated conductors) have to be coated in the possibly shortesttime. Since many compounds only exhibit the desired properties if thefilm is of high crystalline perfection, the requirements on the coatingtechnology are very demanding. Further, for mixed compounds the correctstoichiometric composition has to be guaranteed across the entiredeposition area and for the whole duration of the coating process.

As a rule, the deposition is performed by vacuum coating techniques likesputtering, Laser ablation (PLD), chemical vapor deposition (CVD),molecular beam epitaxy (MBE), or evaporation. For those techniques thatstart from non-conductive, ceramic compounds (targets) (e.g. sputtering,PLD) the volume deposition rate is usually very low. Techniques like CVDor co-evaporation, as described for example in EP 0 282 839 B1, employindividual material sources, where material flows have to be controlledindividually by a complex control. Furthermore, since the materialcomponents do not originate from a single point source and reactsensitively on local physical deposition parameters like substratetemperature or gas pressure, deviations of the film composition on alarge area are inevitable.

The ideal coating technique would use a point source from which materialis emerging with the correct composition at high mass flow, spreadinghomogenously even over long distances, and depositing on a large area.This ideal is realized in good approximation by electron beamevaporation, where a high-energy electron beam is extremely heating andevaporating the target material. For this reason, this method is usedfor many technical coating processes for simple compounds or elements,like e.g. aluminum for reflectors and wrapping foil, or simple oxidesfor optical surface coatings. However, it is problematic to evaporatemixtures of material where the individual components are stronglydiffering in vapor pressure, or compounds that are chemically destroyedupon electron beam irradiation (cracking) or fractionate.

JP 0 12 64 114 A describes such a method for depositing high temperaturesuperconductor films. However, the results achieved therewith are poor.If such mixtures or compounds are evaporated from a single crucible,they fractionate and due to the continuously changing local thermalconditions the composition of the evaporating material changes withtime. This problem can be faced by a rapid deflection of the electronbeam into several, independent crucibles and the respective dwell times.However, this again means accepting the disadvantages of multiple,locally separated sources, i.e. gradients in the composition acrosslarger areas.

For this reason JP 6 11 95 968 A describes an alternative method for thefabrication of alloy coatings, where the alloying components are filledin variable—sized sector—shaped pockets of a rotating evaporationsource. In this way, by fast rotation under a continuous electron beamon temporal average the desired composition can be evaporated from onespot. The problem of this arrangement, however, is that the capacity ofthe crucibles is limited and a continuous refilling is ruled out due tothe rotation. The method is therefore not appropriate for continuouslong—term coating, which requires a large volume of material. The sameapplies for similar devices with revolving electron beam evaporatorsources as described in JP 20 02 097 566 A, which enable selectiveevaporation of different materials, or the arrangement disclosed in JP02 294 479 A, which prevents the electron beam from “digging in” andwhich guarantees an unchanging fresh surface of the evaporationmaterial.

For continuous production the material supply plays a crucial role. Forstatic evaporator crucibles such refilling devices are known e.g. fromJP 61 003 880 A. Evaporation from a static crucible or gradualevaporation even from a crucible in motion leads to fractioning ofcomplex compounds, like e.g. oxidic high temperature superconductors,and to problems with the chemical composition of the coating. The reasonis that within the evaporator crucible no equilibrium is reached becausethe local thermal and chemical conditions are continuously changing.

A possible way out is the so called “flash evaporation” of individualmaterial grains. Thereby small quantities (grains) of evaporationmaterial are evaporated sequentially and quantitatively, i.e.essentially without residues. Thereby the vapor on temporal average overseveral grains is forced to exhibit the same composition as theevaporation material. Generally speaking, the almost instantaneousevaporation of a portion of material is of minor importance forquantitative evaporation compared to the establishment of an equilibriumwithin the evaporation zone between evaporation by the electron beam andthe continuous material supply.

A first attempt for this kind of evaporation is described by Davis etal. in J. Appl. Phys. 66, (1989) 4903. The authors tried to fabricateoxide superconductor films by evaporating a thin line (trace) of powderof the respective evaporation material from front to back by an electronbeam. At the hot front, individual powder grains should continuouslyevaporate in fractions of a second. The results of these experiments,however, were not satisfactory. Since the initial powder materialexhibits a large internal surface and is partially hygroscopic, thegrains absorb a lot of water. Upon strong heating the water evaporatesinstantaneously leading to explosions of the powder grains, which hurlthem out of the evaporation zone instead of transferring them into thegas phase. For this reason a two—step process was used. In a first step,applying the electron beam at much lower power level, the powder wasdegassed and melted into small droplets. In the second step, it wastried to transfer these droplets into the gas phase by flashevaporation.

Davis et al. used the flash evaporation in combination with anotherprocessing step for fabricating the high temperature superconductor, byfirst evaporating the material in the mentioned way in high vacuum andthen re-crystallizing the deposited amorphous material in an oxygenambient, using either a heating device within the evaporation chamber atreduced oxygen pressure (“in situ”), or a furnace with oxygen atatmospheric pressure (“ex situ”).

Because of the above explained processing route of Davis et al. forflash evaporation it is immediately clear that this method is notappropriate for larger quantities of material or for continuousoperation. In addition, the evaporation zone is shifting continuouslyalong the trace. Furthermore, it turned out that the droplets with amass of around 0.1 g were already too big to be transferred into the gasphase instantaneously. Concentration depth profiles of the compositionof a layer which was formed by evaporating a single droplet—in this caseYBa₂Cu₃O₇—exhibit distinct fractioning with strong Ba—enrichment towardsthe film surface. For this reason, the films have to be thermallyannealed and even after that exhibit poor quality.

The problem underlying the present invention is to establish a deviceand a method to deposit a coating material onto a substrate, that can beoperated economically at high rates on the one hand, and results in highquality films on the other hand, and in this way overcomes the mentioneddisadvantages of the state of the art.

3. SUMMARY OF THE INVENTION

According to a first aspect the present invention relates to a devicefor depositing a high temperature superconductor onto a substrate invacuum comprising a refilling device for containing a stock of hightemperature superconductor material, an evaporation device, thatevaporates the high temperature superconductor material within anevaporation zone by means of an energy transferring medium beam, and aconveyor that transports the high temperature superconductor materialcontinuously from the refilling device to the evaporation zone in such away that the high temperature superconductor material delivered into theevaporation zone is evaporated essentially without residues.

With the device according to the invention, equilibrium is reachedwithin the evaporation zone between the continuous evaporation ofmaterial by the energy transferring medium and the continuous materialsupply by the conveyor. Since the evaporation essentially withoutresidues at a constant rate (adjustable by the material supply) occursessentially in equilibrium and from an essentially stationary pointsource, a sophisticated rate control is not necessary and thecomposition of the deposited film is more homogenous across the entiredeposition area than with already known deposition techniques. Further,in the device according to the invention the substrate can be placedvery close to the evaporation zone and can cover a large angle in spaceto increase the evaporation material yield. This is a big advantage overarrangements with several sources (co-evaporation, MBE), which have tokeep a certain minimum distance to limit deviations of the composition.

Preferably the beam of the evaporation device is scanned at least in onedirection across the evaporation zone, so that the high temperaturesuperconductor material transported by the conveyor into the evaporationzone is preferably first preheated and then evaporated.

In a first preferred embodiment the evaporation device comprises anelectron beam evaporator which can be preferably modulated. However,also arrangements for generating other high energy particle beams (e.g.ion beam bombardment) or using Lasers are possible. At present, electronbeams are preferred because they are comparatively cheap and can beeasily modulated.

Preferably the high temperature superconductor material is delivered inform of a line into the evaporation zone, where the line width ispreferably between 3 and 30 mm. The high temperature superconductormaterial is preferably delivered into the evaporation zone as agranulate with a grain size of 0.05-0.5 mm, preferably 0.1-0.5 mm andmost preferably 0.1-0.2 mm.

Granular bulk goods are especially easy for refilling. The givenparameters ensure that the heat capacity of the individual grains of thehigh temperature superconductor material is not too large so that theycan be evaporated sufficiently fast. A similar argument holds even ifthe grains are not individually “flash evaporated”, but are evaporatedalong a somehow longer stretch x, i.e. over a longer period in time. Inany case, the fine granularity is important for sufficient statistics,since the material within an individual grain can thoroughlyfractionate.

The conveyor comprises preferably of a revolving turntable, and/or arotating cylinder, and/or a vibration conveyor, and /or a conveyor belt,and/or a screw conveyor or slide. These embodiments, which are onlynamed exemplarily, allow high rotation—and conveying speed and—with arespective power adjustment of the evaporating device—result in a veryhigh deposition rate in the continuous operation mode. The refillingdevice is preferably realized by a funnel.

The conveyor is preferably cooled, to avoid destruction by the electronbeam. The refilling device, however, is preferably heated and containspreferably a separate pumping device. In a particularly preferredembodiment the refilling device is realized by a funnel which can beheated in its lower section and the separate pumping device is a suctionpipe, which protrudes into the lower section of the funnel. Thepreferred granular high temperature superconductor material, especiallyif it is hygroscopic material, can absorb water, which leads toexplosion of the grains under electron bombardment and thereby to theloss of the material from the evaporation zone. The illustratedpreferred characteristics of the device prevent this and ensure furtherthat the chamber vacuum is not affected. Alternatively, the granulatecan be pre-treated and degassed thermally and can be attached to theconveyor in a sealed cartridge.

According to another preferred embodiment the high temperaturesuperconductor material comprises of a mixture of different compounds,so that during evaporation on temporal average the desired compositionof the high temperature superconductor material is deposited to avoidstatistic fluctuations of the film composition. Further, thereby theaverage composition of the high temperature superconductor material tobe evaporated can be varied flexibly, e.g. to compensate for aninfluence of different sticking coefficients onto the substrate on thestoichiometry. The mixing device can be placed inside or outside thevacuum, or the material is pre-mixed from different components.

Further the device contains preferably means that enable a gas supplyclose to the substrate, as described in DE 19 680 845 C1. Thereby it ispossible to compensate for the loss of gaseous components of theevaporation material during evaporation.

According to a further aspect, the present invention relates to a methodto evaporate a high temperature superconductor coating onto a substratein vacuum, comprising the steps of continuous delivery of granular hightemperature superconductor material into an evaporation zone and theoperation of a beam of an energy transferring medium, so that thedelivered granulate is evaporated in the evaporation zone essentiallywithout residues.

Preferably the granulate is supplied into the evaporation zone in theshape of a line, where the beam of the energy transferring medium isguided over one end of the line, so that the line is scanned essentiallyacross its entire width and over a small section in the direction of theconveying motion.

Further developments of the device and the method according to theinvention are the subject of further depending patent claims.

4. SHORT DESCRIPTION OF THE DRAWINGS

In the following the preferred embodiments of the invention areexplained in detail with reference to the following drawings, whichdepict:

FIG. 1: Schematic sketch of a preferred embodiment of the deviceaccording to the invention viewed from top;

FIG. 2: Schematic cross section of a preferred embodiment of the deviceaccording to the invention with a funnel as refilling device;

FIG. 3: Schematic cross section of a preferred embodiment of the deviceaccording to the invention with electron beam evaporator, materialrefilling, and substrate holder;

FIG. 4: Schematic cross section of a preferred embodiment of the deviceaccording to the invention with electron beam evaporator, substrateholder, and material storage container which can be heated and pumped;

FIG. 5: Detailed drawing of a heatable refilling funnel with suctionpipe;

FIG. 6 a: Evaporation zone of the device (broken line) at the end of thematerial trace. The direction of transport is marked by the arrow.

FIG. 6 b: Power profile of the electron beam along the transportdirection x according to a first embodiment;

FIG. 6 c: Average thickness, respectively quantity D of the materialtrace at the entrance into the evaporation zone;

FIG. 7 a: Power profile of the electron beam in the transport directionaccording to another preferred embodiment;

FIG. 7 b: Thickness profile D(x) of the evaporation material in theevaporation zone if the power profile of FIG. 7 a is employed;

FIG. 7 c: Preferred focusing of the electron beam for the power profileof FIG. 7 a;

FIG. 8 a,b: Schematic drawing of the inclination of the conveyor (FIG. 8a) and the substrate (FIG. 8 b) for compensation of the inclineddirectional pattern of the evaporating material; and

FIG. 9: Combination of two evaporation devices for a symmetricdirectional pattern of the evaporating material.

5. DETAILED DESCRIPTION OF THE INVENTION

In the preferred embodiment of a device according to the invention asdepicted in FIG. 1, a several millimeter to several centimeter widetrace 4 of fine—granular material 13 is placed onto a conveyor realizedin form of a cooled turntable 3 made of material with good heatconductivity, preferably copper, and delivered into an electron beamevaporator 1. For this purpose, the material 13 is applied inwell—measured doses from a big reservoir by a continuously operatingrefilling device 5 onto the conveyor 3 as a line or trace 4 which isseveral millimeters to several centimeters wide.

The conveyor 3 extracts this trace 4 from the refilling device 5 anddelivers it into the hot evaporation zone of an electron beam 2. Therebythe trace 4 is then evaporated continuously and essentially withoutresidues. Therefore the beam 2 can be scanned across the line width oris sufficiently wide. The evaporation rate can be controlled by therotation—or conveying speed of the conveyor 3 and the cross section ofthe line 4. In particular, very high evaporation rates can be realizedin long term operation by respectively high conveying speed and power ofthe electron beam 2.

Quantitative evaporation, i.e. essentially without leaving residues, canbe achieved if within a spatially very narrow evaporation zone of a fewmillimeter length an equilibrium is established between the continuousevaporation of material by the electron beam 2 and the material supply.Therefore, as depicted in FIG. 6 a the electron beam 2 can be scannedacross an area (broken line) covering the tip of the incoming materialtrace 4 completely, and its intensity can be modulated. Modern electronbeam evaporators offer these options.

According to a first embodiment the power of the electron beam 2 ismodulated in such a way (cf. e.g. FIG. 6 b), that the new incomingmaterial is first pre-heated at lower power level and upon advancinginto the hot evaporation zone is first melted and then essentiallycompletely evaporated. At the other end of the evaporation zone thepower P of the electron beam 2 should be such high that essentially noresidues are left on top of the conveying device 3.

FIG. 6 c shows the spatial variation of the thickness D(x) of thematerial trace 4, respectively the average material quantity of thetrace 4. Even if in this arrangement the various components of theevaporation material originate from different sections of the hotevaporation zone, after a short initial phase upon continuous operationan equilibrium is established, so that on average always the compositiongiven by the evaporation material is evaporated. Since the area coveredby the electron beam 2 extends only a few millimeters in the x-directionof the incoming material trace 4, the ideal concept of a point source isrealized in good approximation.

To achieve high evaporation rates it has turned out as advantageous toapply the material trace 4 up to several centimeters wide (y-direction)and very thin. This avoids the formation of excessively large dropletswhen the material 4 melts in the entrance region of the hot evaporationzone, so that statistic variations are kept small.

With the device and the method according to the embodiments of thepresent invention oxide high temperature superconductor films ofYBa₂Cu₃O₇ (YBCO), DyBa₂Cu₃O₇ (DyBCO), and NdBa₂Cu₃O₇ (NdBCO) have beenfabricated. However, the device and method can also be used to fabricatethe other coatings named in the introduction. In general, as hightemperature superconductor preferably RBa₂Cu₃O₇ (R=yttrium, or anelement with atomic number 57 to 71, or a mixture of these elements) ispossible. Granular material with a slight copper excess and 0.1 mm grainsize has been applied by a funnel 5 in shape of a 3-30 mm wide, and0.1-1 mm thick trace 4 onto a copper turntable, and was extracted fromthe bottom of the funnel 5 by continuous rotation, and delivered to theelectron beam 2. Oxygen was directly supplied at the about 680° C. hotsubstrate 7, which could be moved to prevent thickness variations, sothat an epitaxial superconductor film was deposited at a deposition rateof 0.4 nm/s. However, by adjusting the rotation speed of the turntable 3and the power of the electron beam evaporator 2 evaporation rates inexcess of 2 nm/s could be realized without problems. The superconductorfilms fabricated on MgO single crystals exhibit transition temperaturesof 87 K and critical current densities in excess of 2 MA/cm², which israted as excellent quality for applications.

The granulate to be evaporated should preferably have a grain sizebetween 50 μm and 500 μm. If the grains are smaller or bigger, it ispossible, especially at higher evaporation rates, that they aredispersed by the electron beam 2 and are therefore not evaporatedproperly. These eruptions can constitute a loss of material anddeviations from the stoichiometry. If this occurs actually, however,depends on the setup of the entire system.

The stoichiometry is particularly critical for high temperaturesuperconductors. Preferably it has to be maintained within 1-2% accuracyto reproduce particularly good superconducting properties. This is amuch more stringent requirement than necessary for example forfabrication of glasses or alloys. The repetition frequency for the scanof the electron beam 2 should be preferably as high as possible, butpreferably at least 50 Hz, to minimize the dispersion of the evaporationmaterial 4 by eruptions at higher evaporation rate.

To control the process a continuous measurement of the evaporation rateof the high temperature superconductor is preferred. For a long termdeposition process quartz rate monitors are only poorly applicable,since they are saturated rapidly. Instead, the rate can be preferablymeasured by atomic absorption spectroscopy (AAS) (not shown). For that,however, at least one component of the evaporating material 4 must notbe present in molecular form as an oxide, but in atomic form as anelement.

It has turned out that upon electron evaporation of high temperaturesuperconductors the Cu—component is always present in atomic form.Therefore, it is advantageous to determine the total evaporation rate ofthe superconductor by using the AAS of the Cu—line. At the aimed highevaporation rates and large diameters of the vapor beam for large areadeposition, however, there may arise the problem, that the absorptionline is saturated. This can be preferably solved by a partial shading ofthe vapor at the location of the measurement, so that the absorptionpreferably occurs only in a multitude of well-defined sections of thelight beam. The positions of the sections can be preferably chosen insuch a way that the respective Doppler shifts of the Cu—absorption lineall together cover the whole spectral width of the light beam. Thelengths of the sections are preferably chosen in such a way that theabsorption at the desired evaporation rate is approximately 30%.

Preferably, in combination with the actual high temperaturesuperconductor layer also further auxiliary layers of different oxidematerials are deposited as a base or cap layer. They serve as diffusionbarriers, for establishing texture, as seed layer, or as protectionagainst environmental influence etc. For technical and economic reasonsit is preferred to deposit them onto the substrate 7 sequentially withthe actual superconductor layer in situ, i.e. without breaking thevacuum. For this reason it is advantageous if it is possible toevaporate different materials sequentially with the same device, e.g. byplacing several storage containers 5, which can each be closed at theirbottom outlet, next to each other on top of the conveyor 3.

For evaporation of a certain material one of the storage containers 5 isopened and the scanning area of the electron beam 2 is adjusted to therespective material trace 4. The closure at the outlet of the storagecontainer 5 can be e.g. realized by a plug (not shown), located insidethe storage container 5. For fine-grain material the plug just has toblock the outlet and does not have to seal it tightly. Hence, it can belifted (outlet open) or lowered (outlet closed) by a simple mechanism.For lowering, the residual material underneath the plug has to bepreferably removed from the outlet by operating of the conveyor 3,before the evaporation of the new material is started. If space isrestricted, it may be advantageous not to place the various storagecontainers permanently on top of the conveyor 3, but to use a mechanismto position only a partial number of storage containers, preferably onlya single storage container 5 on top of the conveyor 3. The mechanism canbe for example, a revolver, a magazine, or a single lowering device (notshown) for each container.

For further description of variations of the device and the methodaccording to the invention, the currently particularly preferredexamples 1-10 are explained in more detail in the following:

EXAMPLE 1

Granular evaporation material 13 is conducted by a trapezoid funnel 5onto a rotating, water—cooled copper turntable 3 of an electron beamevaporator 1. Due to the rotation of the turntable 3 a fine trace ofmaterial 4 is extracted at the bottom of the funnel 5 and delivered tothe electron beam 2 on the opposite side. The power and focus of theelectron beam 2 is adjusted in such a way, that upon entering the hotevaporation zone the arriving grains of the evaporation materialevaporate rapidly and essentially without residues, i.e. they evaporatequantitatively. The vapor spreads unimpeded within the high vacuumchamber 6 and condenses onto a substrate 7 which can be heated ifnecessary (cf. Substrate heater 8 in FIG. 3). If required, a reactivegas can also be introduced into the chamber 6 or supplied directly atthe substrate 7 by an appropriate device 9, 10.

In contrast to the mentioned state of the art of Davis et al. the flashevaporation is used as a one-step technique for fabricating hightemperature superconductors.

Therefore, the oxygen necessary for oxidation and crystal formation issupplied directly during the material deposition, using the device 9, 10according to FIG. 3 and by increasing the substrate temperature by aheater 8.

Additionally, the flash evaporation of high temperature superconductorscan be used in combination with a moving substrate 7, for example byrotating the substrate 7 in FIGS. 3 and 4 around a vertical axis (notshown). This has the advantage of a more homogeneous stoichiometry on alarge area, which is particularly critical for high temperaturesuperconductors. Beyond that, the motion of the substrate isadvantageous for depositing on a large number of substrates (e.g. waferdeposition in a series production), or very large substrates (e.g.substrate plates for fault current limiters), or very long tape (“coatedconductors”), which are continuously transported through the evaporationzone without interrupting the evaporation process.

EXAMPLE 2

The setup corresponds to that described in example 1. The granulate 13,however, originates from a closed storage container 5 which can beheated by heater elements 11 and which can be pumped at through apumping neck to remove released residual gas. With such a setupevaporation rates of 5 nm/s have been achieved. For this, a preferredgrain size of 100-200 μm has been used and the preferred scanningrepetition frequency was 90 Hz. The stoichiometry deviation on an areaof 20 cm×20 cm was merely 1%.

EXAMPLE 3

The setup corresponds to that described in example 1. The granulate 13,however, is supplied through a funnel 5, which is heated only in itsbottom outlet section by heater elements 11. The thereby released watervapor is pumped away directly at its origin by a suction pipe 12,preferably with a sieve in front of the inlet (not shown).

EXAMPLE 4

Granular evaporation material 13 is conducted by a conveyor belt, ascrew conveyor or a similar conveyor like a slide (not shown) onto arotating, water—cooled copper turntable 3 of an electron beamevaporator. Due to the rotation of the turntable 3 a fine trace ofmaterial 4 is delivered to the electron beam 2 on the opposite side. Thepower and focus of the electron beam 2 is adjusted in such a way, thatupon entering the hot evaporation zone the arriving grains of theevaporation material 13 evaporate rapidly and essentially withoutresidues, i.e. they evaporate quantitatively. The vapor spreadsunimpeded within the vacuum chamber 6 and condenses onto a substrate 7which can be heated by a substrate heater 8 if necessary. If required, areactive gas can also be introduced into the chamber or supplieddirectly at the substrate 7 by an appropriate device 9, 10.

EXAMPLE 5

Granular evaporation material 13 is applied by a refilling device, e.g.a trapezoid funnel 5, onto a rotating, water—cooled drum (not shown) anddelivered as a fine line to the electron beam 2 of an electron beamevaporator. The power and focus of the electron beam 2 is adjusted insuch a way, that upon entering the hot evaporation zone the arrivinggrains of the evaporation material evaporate rapidly and essentiallywithout residues, i.e. they evaporate quantitatively. The vapor spreadsunimpeded within the high vacuum chamber 6 and condenses onto asubstrate 7 which can be heated by a substrate heater 8 if necessary. Ifrequired, a reactive gas can also be introduced into the chamber orsupplied directly at the substrate 7 by an appropriate device 9, 10.

EXAMPLE 6

Granular evaporation material 13 is applied by a refilling device, e.g.a trapezoid funnel 5, onto a water—cooled vibration conveyer anddelivered as a fine line to the electron beam 2 of an electron beamevaporator 1. The power and focus of the electron beam 2 is adjusted insuch a way, that upon entering the hot evaporation zone the arrivinggrains of the evaporation material evaporate rapidly and essentiallywithout residues, i.e. they evaporate quantitatively. The vapor spreadsunimpeded within the high vacuum chamber 6 and condenses onto asubstrate 7 which can be heated by a substrate heater 8 if necessary. Ifrequired, a reactive gas can also be introduced into the chamber 6 orsupplied directly at the substrate 7 by an appropriate device 9, 10.

EXAMPLE 7

Granular evaporation material 13 is applied by a refilling device, e.g.a trapezoid funnel 5, onto a cooled conveyer belt and delivered as afine line to the electron beam 2 of an electron beam evaporator. Thepower and focus of the electron beam is adjusted in such a way, thatupon entering the hot evaporation zone the arriving grains of theevaporation material evaporate rapidly and essentially without residues,i.e. they evaporate quantitatively. The vapor spreads unimpeded withinthe high vacuum chamber 6 and condenses onto a substrate 7 which can beheated by a substrate heater 8 if necessary. If required, a reactive gascan also be introduced into the chamber 6 or supplied directly at thesubstrate 7 by an appropriate device 9, 10.

EXAMPLE 8

Material feeding and transport correspond to one of the previousexamples 1-7. The material trace 4 can have a width of severalcentimeter. The electron beam 2 is scanned over an area, which coversthe width of the arriving material trace 4 completely, e.g. arectangular area as shown in FIG. 6 a. Thereby the power P of theelectron beam 2 is modulated in such a way, that with proceedingposition the arriving material is first pre-heated, melted, and thencompletely evaporated. An appropriate power profile is shown for examplein FIG. 6 b. The shape of the profile (e.g. linear, exponential,sinusoidal, etc.) can be chosen appropriately. In this context it ismainly important that the peak power is set sufficiently high, so thatall the material evaporates essentially without residues. In this case,for example a thickness profile as shown in FIG. 6 c may be established.

EXAMPLE 9

According to a further embodiment a preferable 2—stage profile is usedwith essentially two power levels for the electron beam 2 as shown inFIG. 7 a. Thereby the power level P₁ is preferably chosen in such a waythat the material is annealed but the temperature is not sufficient toevaporate components of the high temperature superconductor,particularly Cu. The power level P₂ is preferably chosen such that, thehigh temperature superconductor is evaporated quantitatively. Thetransition width Δx between the two zones is preferably as narrow aspossible, so that the material evaporates instantaneouslyquantitatively. Then, a linear slope of the thickness profile D(x)according to FIG. 7 b is established.

If the transition width Δx between the two power zones is notsufficiently narrow, there is a danger, that the upper edge of the slope(i.e. the boundary between the two power zones) is rounded andparticularly the copper component of the granulate evaporates with afalse directional pattern. To achieve a narrow transition the electronbeam has to be preferably focused in such a way, that while scanning itreaches the smallest possible width, when it is located at the upperedge of the slope. This is depicted schematically in FIG. 7 c.

The inclination angle α of the slope in FIG. 7 b is determined by theconveying velocity of the evaporation material v_(F) and the evaporationspeed of the material trace dD/dt according to tan α=(dD/dt)/v_(F).Thereby the angle α can be adjusted for every evaporation speed by theconveying velocity.

Since the evaporation material evaporates preferably from the slope, thedirectional pattern of the evaporating material is inclined by the angleα against the normal of the conveying device (cf. FIG. 7 b). In mostcases the inclination is disadvantageous for the deposition. Therefore,α should preferably not be bigger than 20°. On the other hand, if theangle α becomes too flat, at a given initial thickness D₀ of thematerial trace the length L of the evaporation zone increases accordingto L=D₀/tan α. Preferably, L should not be longer than 10 mm, that thematerial evaporates sufficiently point—like and no noticeable gradientsin the stoichiometry result on the substrate. Hence, at a typicalthickness D₀=1 mm preferably α should not be smaller than 6°.

The inclination of the directional pattern of the evaporating materialat the angle α can be compensated by inclining the entire conveyor 3including the conveyor trace 4 by essentially the same angle in theopposite direction. This is shown schematically in FIG. 8 a. However, ifthe inclination angle is too big, the transport of the evaporationmaterial can be impeded when the trace 4 on top of the conveying device3 begins slipping. This problem is avoided by another option tocompensate the angle α by inclining the substrate 7 corresponding. Thisis shown schematically in FIG. 8 b.

EXAMPLE 10

To arrive at a symmetric directional pattern of the evaporating materialdespite the inclination at an angle α, according to another embodimenttwo or more evaporation devices can be employed, too. E.g. twoevaporation devices can be preferably placed next to each other, so thatthe evaporation zones are facing each other. This is shown in FIG. 9.The evaporation rates of both devices should preferably coincide in thiscase.

LEGEND OF REFERENCE NUMBERS

-   -   1 Electron gun    -   2 Electron beam    -   3 Turntable (rotating)    -   4 Material trace (line)    -   5 Refilling device (funnel, storage container)    -   6 Vacuum chamber    -   7 Substrate    -   8 Substrate heater    -   9 Reactive gas supply    -   10 Gas inlet    -   11 Heating element    -   12 Suction pipe    -   13 Granulate

1. Device for continuous evaporation of a high temperaturesuperconductor onto a substrate in a vacuum comprising: a. a refillingdevice with a stock of high temperature superconductor material; b. anevaporation device which evaporates the high temperature superconductormaterial in an evaporation zone by a beam of an energy transferringmedium; c. a conveyor which transports the high temperaturesuperconductor material from the refilling device to the evaporationzone; wherein d. the evaporation device is adapted to pre-heat thehigh-temperature superconductor material in a first part of theevaporation zone by a first energy of the beam of energy transferringmedium and to evaporate the pre-heated high-temperature superconductormaterial in a second part of the evaporation zone by a second energy ofthe beam of energy transferring medium, wherein said second energy isgreater than said first energy.
 2. Device according to claim 1, furthercomprising a means to scan the beam of the evaporator in at least onedirection over the evaporation zone.
 3. Device according to claim 2,wherein the means scans the beam at a repetition frequency of greaterthan about 50 Hz and preferably at about 90 Hz.
 4. Device according toclaim 1, further comprising a means to first preheat and then evaporatethe high temperature superconductor material delivered to theevaporation zone by the conveyor.
 5. Device according to claim 4, wherethe evaporation device comprises at least two power levels for the beam,with a narrow transition width between the first and the second powerlevel to achieve a linear gradient of a thickness profile of a deliveredhigh temperature superconductor material.
 6. Device according to claim5, wherein the conveying speed of the conveyor can be adjusted tosatisfy at least one of the conditions that an angle of a slope α isless than about 20°, and the length of the evaporation zone is less thanabout 10 mm.
 7. Device according to one of the claims 5 or 6, whereinthe beam of the energy transferring medium can be focused in such a waythat while scanning it reaches a minimum width when it is focusedapproximately at the upper edge of the slope.
 8. Device according toclaim 1, wherein the conveyor and the substrate can be tilted tocompensate for an inclined directional pattern of the materialevaporating from the conveyer.
 9. Device according to claim 1, whereinthe evaporation device comprises an electron beam evaporator which canbe modulated.
 10. Device according to claim 1, wherein the hightemperature superconductor material is conveyed into the evaporationzone in the shape of a line with a width of greater than about 3 mm andless than about 30 mm.
 11. Device according to claim 1, wherein theconveyor transports the high temperature superconductor material to theevaporation zone as a granulate with a grain size of greater than about0.1 mm and less than about 0.2 mm.
 12. Device according to claim 1,wherein the conveyor can be cooled and comprises at least one of arotating turntable, rotating drum, a vibration conveyor, a conveyorbelt, a screw conveyor, and a slide.
 13. Device according to claim 1,wherein the refilling device is designed as a funnel and can be heated.14. Device according to claims 1, wherein the refilling device has aseparate pumping device.
 15. Device according to claim 14, wherein therefilling device is designed as a funnel which can be heated in a bottomsection, and the separate pumping device is designed as a suction pipewhich protrudes into the bottom section of the funnel.
 16. Deviceaccording to claim 1, wherein the high temperature superconductormaterial is a mixture of different compounds, so that upon evaporationon temporal average the desired composition of the high temperaturesuperconductor material is deposited.
 17. Device according to claim 1,further comprising a means to supply a gas close to the substrate. 18.Device according to claim 1, further comprising a means to heat and movethe substrate relative to the evaporation zone.
 19. Device according toclaim 1, further comprising a means to measure an evaporation rate byatomic absorption spectroscopy.
 20. Device according to claim 19,further comprising a means to partially shade the vapor of the hightemperature superconductor material where a measuring light beam islocated to avoid saturation of the absorption line.
 21. Device accordingto claim 1, further comprising a second refilling device having sourcematerial for an auxiliary layer of the high temperature superconductorfilm.
 22. Device according to claim 21, further comprising a means forconnecting said second refilling device to the first refilling device,and for holding a stock of high temperature superconductor materialsequentially with the conveyor.
 23. Method for continuously evaporatinga high temperature superconductor coating onto a substrate in a vacuumcomprising the steps of: a. continuously conveying a granulate of a hightemperature superconductor material into a evaporation zone; b.pre-heating the high-temperature superconductor material in a first partof the evaporation zone by a first energy of the beam of energytransferring medium; and c. evaporating the pre-heated high-temperaturesuperconductor material in a second part of the evaporation zone by asecond energy of the beam of energy transferring medium so that thedelivered granulate is evaporated essentially without residues withinthe evaporation zone.